Lens for shooting concerts?
 

hey do you have a low f stop lenses you recommend....specially I am looking for something that i can use when shooting rock bands in low light clubs.

Generally, any f/2.8 lens works here.

Too much lower, and the depth is too shallow to use feasibly in a hand-held situation. Lower (faster) lenses will give better viewfinder clarity, and the 2.8 may be sharper since the lens would be stopped down. Max aperture is often not the sharpest range of the lens. A good prime of 50mm, 85mm or 105mm would maybe look nice, shot at f/2.8.

When I shoot concerts, it's usually with a modern high-ISO body, such as the Nikon D3 or the Canon 5D (or 5D MkII). Those give low noise and allow for faster shutters to catch the action of the stage.

Honestly, most stages are lit up enough that I was shooting ISO 800 Fuji film with f/2.8 lenses, and the photos were publish-quality for newspapers, in approximate 5x7 to 8x10 sizes. I could push the film to ISO 1600 and get slightly grainier but potentially sharper (from stop-action) images. This was in the late 1990s.

Canon L glass would be great, or even the Sigma 70-200 you're already using. It mostly depends on how close to the stage you plan to be.

Right now, I am strapped for cash so I was looking at a Canon EF 50mm f/1.8 II
its a cheaper lens but according to some digital photography sites is a good entry level lens.
Im looking for something that will shoot in really low light. like a bar. my current lens is a Canon EF 24-105mm f/4L IS

That lens will work quite nicely. On a crop body, it will be about 75mm equivalent lens. It's very affordable, and very nice.

I might still look at slight longer lengths, however. Maybe locate a good f/2.8 or lower lens in the 80-100mm range, be it an 85mm, a 105mm, or some other length.

The 24-105 f/4 might work, but at reduced shutter speeds and/or with higher ISO. In many conditions, you'd simply pop a flash, but concerts have unique mood lighting that you don't want to lose that way.